RF current return path for a large area substrate plasma reactor

ABSTRACT

An apparatus for providing a return current path for RF current between a chamber wall and a substrate support is provided comprising a low impedance flexible curtain having a first end and a second end, the first end adapted to be electrically connected to the chamber wall and the second end adapted to be connected to the substrate support, wherein the curtain further comprises at least one fold in the curtain material, located an axial distance between the first end and the second end, and at least one perforation cut into the curtain proximate the second end.

FIELD OF THE INVENTION

[0001] The present invention generally relates to processing equipmentused in the processing of large area substrates, and more particularlyrelates to an RF current return path for such equipment.

BACKGROUND OF THE INVENTION

[0002] Liquid crystal displays or flat panels are commonly used foractive matrix displays such as computer and television monitors,personal digital assistants (PDAs), cell phones and the like. Generally,flat panels comprise two glass plates having a layer of liquid crystalmaterial sandwiched therebetween. At least one of the glass platesincludes at least one conductive film disposed thereon that is coupledto a power supply. Power supplied to the conductive material film fromthe power supply changes the orientation of the liquid crystal material,creating patterns such as text or graphics that may be seen on thedisplay. One fabrication process frequently used to produce flat panelsis plasma enhanced chemical vapor deposition (PECVD).

[0003] Plasma enhanced chemical vapor deposition is generally employedto deposit thin films on a glass substrate such as those utilized tofabricate flat panels. Plasma enhanced chemical vapor deposition isgenerally accomplished by introducing a precursor gas into a vacuumchamber that contains the substrate. The precursor gas is typicallydirected through a distribution plate situated near the top of thechamber. The precursor gas in the chamber is energized (e.g., excited)into a plasma by applying RF power to the chamber from one or more RFsources coupled to the chamber. The excited gas reacts to form a layerof material on a surface of a substrate that is positioned on atemperature controlled substrate support. The substrate support istypically grounded to the chamber body. In applications where a layer oflow temperature polysilicon is deposited onto the substrate, thesubstrate support may be heated in excess of 400 degrees Celsius.Volatile by-products produced during the reaction are pumped from thechamber through an exhaust system.

[0004] During this process, the substrate support is biased negativelywith respect to the plasma to further enhance deposition. This isaccomplished by providing a bias voltage to an electrode within thesubstrate support assembly. With a negative bias voltage applied to thesubstrate support, positively ionized material in the plasma isattracted to and deposits on the substrate in a highly perpendicularmanner, improving the deposition characteristic known as “stepcoverage”.

[0005] Ideally, the bias voltage on the substrate support remains stableas the ionized material is deposited onto the substrate. A stable biasvoltage results in ionized deposition material being drawn and depositeduniformly across the width of the substrate. Voltage stability isrealized when there is no appreciable voltage drop due to currentflowing from the substrate support to ground. If the voltage drop issignificant, the differential may induce plasma to strike between twopoints at substantially different voltages, such as the substratesupport (at a high potential) and a nearby grounded feature (such as achamber wall), thereby damaging the processing environment and possiblycontaminating the substrate. Some systems employ a low impedance strapto couple the substrate support to the chamber body to facilitategrounding of the substrate support.

[0006]FIG. 10 is a simplified perspective, cutaway view of an exemplaryconventional processing chamber 30 having a plurality of straps 20 forelectrically coupling a substrate support 40 to a wall 32 or bottom 34of the chamber 30. Four of eight straps 20 are shown in FIG. 10, twostraps 20 coupled to each edge of the substrate support 40.

[0007] The substrate support 40 typically includes a plurality of liftpins 52, some of which are disposed along the edge of the substratesupport 40 to lift the edges of the substrate during transfer. A liftplate 50 is disposed below the substrate support 40 and may bevertically actuated to extend the lift pins 52 through the substratesupport 40 to space a substrate from the substrate support duringsubstrate transfer.

[0008] Each of the straps 20 includes a first and second flexures 22, 24separated by a bend 26. The straps 20 are generally aligned with theperimeter of the substrate support 40 and spaced to provide room for thelift pins 52 to extend below the substrate support 40. In order toprovide clearance of a lift plate 50 positioned below the substratesupport 40 that is utilized to vertically actuate the lift pins 52, thebend 22 of each strap 20 is oriented perpendicular to the proximate edgeof the substrate support 40 (i.e., the edge of the support the strap iscoupled to) to keep the bend 26 of the strap 20 from being positionedfurther inward relative to the substrate support 40 than the flexures22, 24. As the straps 20 cannot extend into the area occupied by thelift plate 50 and lift pins 52, the number and size of the straps 20 arelimited to the number that may be linearly aligned and nested along theedge of the substrate support 40, while remaining clear of those liftpins 52 positioned along the edge of the substrate support 40.

[0009] While this configuration has proven to be effective and reliablefor smaller scale applications, it is less effective for larger areaglass substrate processing applications which necessitate higher currentflow for adequate grounding. As the next generation of large areasubstrates utilized for flat panel fabrication approaches 1100 mm×1300mm, with even larger sizes envisioned for the near future, the substratesupports utilized to process these large area substrates have increasedin size as well and would benefit from increased grounding capacity notcurrently available from conventional designs. The conductive strapssuch as those described above cannot be coupled between the processingchamber and the substrate support with sufficient density to adequatelylimit the voltage drop between the processing chamber and substratesupport in such large scale processing applications. Additionally,because the straps are spaced around the perimeter of the substratesupport to leave gaps for the lift pins and if the gaps are sufficientlywide, those portions of the substrate support between the straps may bebiased at a higher potential relative to those portions that aredirectly coupled to a strap, which may adversely effect depositionuniformity.

[0010] Therefore, there is a need for a reliable low-impedance RFcurrent return path suitable for use in large area substrate processingapplications.

SUMMARY OF THE INVENTION

[0011] Embodiments of the invention generally provide an RF currentreturn path for large area substrate processing. In one embodiment, anapparatus for providing an RF current return path between a processingchamber and a substrate support includes a low impedance flexiblecurtain having a first end adapted to be electrically connected to theprocessing chamber and a second end adapted to be connected to thesubstrate support, wherein the curtain further comprises at least onefold in the curtain material, located between the first end and thesecond end, and at least one perforation formed through the curtainproximate the second end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the above recited embodiments of theinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings illustrate only typical embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

[0013]FIG. 1 is a cross sectional view of one embodiment of a processingsystem having a ground curtain of the present invention;

[0014]FIG. 2 is a side cross sectional view of one embodiment of an RFground curtain according to the present invention;

[0015]FIG. 3 is an enlarged partial side cross sectional view of anupper end of the ground curtain of FIG. 2;

[0016]FIG. 4 is a top cross sectional view of one embodiment of a clampring for use in the connection assembly of FIG. 3;

[0017]FIG. 5 is an isometric view of one embodiment of an RF groundcurtain and connection assemblies according to the present invention;

[0018]FIG. 6 is an isometric view of one embodiment of an RF groundcurtain;

[0019]FIG. 7 is a cross sectional view of a second embodiment of an RFground curtain according to the present invention;

[0020]FIG. 8 is a cross sectional view of a second embodiment of aprocessing system that may be advantageously adapted to benefit from thepresent invention;

[0021]FIG. 9 is a cross sectional view of a third embodiment of aprocessing system that may be advantageously adapted to benefit from thepresent invention;

[0022]FIG. 10 is a partial cross sectional view of a prior artprocessing system having an RF current return path.

[0023] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon to the figures.

DETAILED DESCRIPTION

[0024] The invention generally provides an RF current return path forsystems supporting large area substrates. The invention isillustratively described below in reference to a plasma enhancedchemical vapor deposition (PECVD) system, such as those commerciallyavailable from AKT, a division of Applied Materials, Inc. of SantaClara, Calif. However, it should be understood that the invention hasutility in other system configurations such as physical vapor depositionsystems, etch systems and other processing systems in which providing alow-impedance RF current return path between a substrate support and achamber housing the substrate support is desired.

[0025]FIG. 1 is a cross sectional view of one embodiment of a plasmaenhanced chemical vapor deposition system 100 having one embodiment of aground curtain 184 that provides a low-impedance path between asubstrate support assembly 138 and ground. The system 100 generallyincludes a grounded chamber 102 coupled to a gas source 104 and a powersource 122. The chamber 102 has sidewalls 106, a bottom 108 and a lidassembly 110 that define a process volume 112. The process volume 112 istypically accessed through a port (not shown) in the sidewall 106 thatfacilitates movement of a large area glass substrate 140 (hereinafterreferred to as “substrate 140”) into and out of the chamber 102. Thesidewalls 106 and bottom 108 are typically fabricated from a unitaryblock of aluminum or other material compatible with processing. The lidassembly 110 contains a pumping plenum 114 that couples the processvolume 112 to an exhaust port that is coupled to various pumpingcomponent (not shown).

[0026] The lid assembly 110 is supported by the sidewalls 106 and can beremoved to service the chamber 102. The lid assembly 110 is generallycomprised of aluminum. A distribution plate 118 is coupled to aninterior side 120 of the lid assembly 110. The distribution plate 118 istypically fabricated from aluminum. The center section of thedistribution plate 118 includes a perforated area through which processand other gases supplied from the gas source 104 are delivered to theprocess volume 112. The perforated area of the distribution plate 118 isconfigured to provide a uniform distribution of gases passing throughthe distribution plate 118 into the chamber 102. The power source 122 iscoupled to the distribution plate 118 to provide an electrical bias thatenergizes the process gas and sustains a plasma in the interior volume112 below the gas distribution plate 118 during processing.

[0027] The heated substrate support assembly 138 is centrally disposedwithin the chamber 102. The support assembly 138 supports the substrate140 during processing. The substrate support assembly 138 generallyincludes an electrically conductive body 124 that is generally polygonalin shape and covered with an electrically insulative coating (not shown)over at least the portion of the body 124 that supports the substrate140. The coating may also cover other portions of the body 124.

[0028] The support body 124 may be fabricated from metals or othercomparably electrically conductive materials. The insulative coating maybe a dielectric material such as an oxide, silicon nitride, silicondioxide, aluminum dioxide, tantalum pentoxide, silicon carbide orpolyimide, among others, which may be applied by various deposition orcoating processes, including, but not limited to, flame spraying, plasmaspraying, high energy coating, chemical vapor deposition, spraying,adhesive film, sputtering and encapsulating.

[0029] In one embodiment, the substrate support assembly 138 includes analuminum body 124 that encapsulates at least one embedded heatingelement 132 and a thermocouple (not shown). At least a first reinforcingmember 116 may be embedded in the body 124 proximate the heating element132. A second reinforcing member 166 may be disposed within the body 124on the side of the heating element 132 opposite the first reinforcingmember 116. The reinforcing members 116, 166 may be comprised of metal,ceramic or other stiffening materials.

[0030] The heating element 132, such as an electrode disposed in thesupport assembly 138, is coupled to a power source 130 and controllablyheats the support assembly 138 and substrate 140 positioned thereon to apredetermined temperature. Typically, the heating element 132 maintainsthe substrate 140 at a uniform temperature of about 150 to at leastabout 460 degrees Celsius during processing.

[0031] Generally, the support assembly 138 has a lower side 126 and anupper side 134 that supports the substrate 140 thereon. The lower side126 has a stem cover 144 coupled thereto. The stem cover 144 generallyis an aluminum ring coupled to the support assembly 138 that provides amounting surface for the attachment of a stem 142 thereto.

[0032] Generally, the stem 142 extends from the stem cover 144 andcouples the support assembly 138 to a lift system 139 that moves thesupport assembly 138 between an elevated process position (as shown) anda lowered position that facilitates substrate transfer. A bellows 146provides a vacuum seal between the chamber volume 112 and the atmosphereoutside the chamber 102 while facilitating the vertical movement of thesupport assembly 138. The stem 142 additionally provides a conduit forelectrical and thermocouple leads between the support assembly 138 andother components of the system 100.

[0033] The support assembly 138 additionally supports a circumscribingshadow frame 148. Generally, the shadow frame 148 prevents deposition atthe edge of the substrate 140 and support assembly 138 so that thesubstrate 140 does not stick to the support assembly 138.

[0034] The support assembly 138 has a plurality of holes 128 disposedtherethrough that accept a plurality of lift pins 150. The lift pins 150are typically comprised of ceramic or anodized aluminum. Generally, thelift pins 150 have first ends 160 that are substantially flush with orslightly recessed from an upper side 134 of the support assembly 138when the lift pins 150 are in a normal position (i.e., retractedrelative to the support assembly 138). The first ends 160 are generallyflared to prevent the lift pins 150 from falling through the holes 128.Additionally, the lift pins 150 have a second end 164 that extendsbeyond the lower side 126 of the support assembly 138. As the supportassembly 138 is lowered to a transfer position, the lift pins 150 comein contact with the bottom 108 of the chamber 102 and are displacedthrough the support assembly 138 to project from the upper side 134 ofthe support assembly 138, thereby placing the substrate 140 in aspaced-apart relation to the support assembly 138.

[0035] In one embodiment, lift pins 150 a, 150 b of varying lengths areutilized so that they come into contact with the bottom 108 and areactuated at different times. For example, long lift pins 150 a spacedaround the outer edges of the substrate 140, combined with relativelyshorter lift pins 150 b spaced inwardly from the outer edges toward thecenter of the substrate 140, allow the substrate 140 to be graduallylifted from its outer edges to its center. In another embodiment, liftpins 150 a, 150 b of a uniform length are utilized, but the bottom 108of the chamber 102 comprises bumps or plateaus 182 positioned beneaththe outer lift pins 150 a, so that the outer lift pins 150 a areactuated before the inner lift pins 150 b. Alternatively, the chamberbottom 108 may comprise grooves or trenches positioned beneath the innerlift pins 150 b, so that the inner lift pins 150 b are actuated afterthe outer lift pins 150 a.

[0036] The support assembly 138 is generally grounded such that an RFpower supplied by the power source 122 to the distribution plate 118 (orother electrode positioned within or near the lid assembly 110 of thechamber 102) may excite the gases disposed within the process volume 112between the support assembly 138 and the distribution plate 118. The RFpower from the power source 122 is generally selected commensurate withthe size of the substrate 140 to drive the chemical vapor depositionprocess.

[0037] The curtain 184 provides an RF current return path between thesupport assembly 138 and chamber 102. The curtain 184 generallycomprises a first end 186, a second end 188, and at least one bend 190.The first end 186 is electrically connected to one of the chamber walls106, 108, while the second end 188 is electrically connected to thesupport assembly 138, typically to the lower side 126 of the conductivebody 124.

[0038] A first flexure 192 extends from the bend 190 toward the firstend 186, and a second flexure 194 extends from the bend 190 toward thesecond end 188. The flexures 192, 194 are substantially quadrilateral inshape and allow for vertical movement of the support assembly 138relative to the chamber bottom 108.

[0039] The curtain 184 may extend continuously around the entire supportassembly 132 or a portion of the perimeter of the body 124. In oneembodiment, a single curtain 184 extends continuously aroundsubstantially the full perimeter of the body 124 (e.g., so that thecurtain 184 contacts each edge of the polygonal body 124).Alternatively, a plurality of curtains 184 may be positioned adjacent toone another to extend around substantially the full perimeter of thebody 124, wherein at least one curtain is coupled to each edge of thepolygonal support assembly 132. In a further embodiment, severalcurtains 184, each having a width of at least twelve inches, arepositioned one on each edge of a polygonal body 124.

[0040] The curtain 184 is comprised of a flexible, low impedanceconductive metal that is resistant to processing and cleaningchemistries. In one embodiment, the curtain 184 is comprised of aluminumand is approximately 0.008 to 0.016 inch thick. Alternatively, thecurtain 184 may comprise titanium, stainless steel, or a flexiblematerial that is coated with a conductive metallic coating.

[0041] The curtain 184 significantly shortens the return path for RFcurrent to ground as compared to conventional grounding techniques.Current passes from the plasma to the substrate 140, which is inelectrical contact with the conductive body 124 of the support assembly138. The lower side 126 of the body 124 is in electrical contact withthe curtain 184, so that the current passes from the body 124 throughthe curtain 184 and to the chamber wall 106, 108, which is connected toground. Furthermore, the curtain 184 provides a larger current carryingarea than existing conductive strap designs, making them ideallysuitable for use in large area processing applications. The shorterdistance and larger current carrying capacity of the curtain 184 resultsin a much lower voltage differential between the surface of the supportassembly 138 and the grounded chamber 102, thereby substantiallyreducing the likelihood of plasma ignition below the substrate supportassembly 138 that may sputter unwanted contaminants in the chamber 102.

[0042]FIG. 2 is a cross sectional view of the curtain 184. In oneembodiment, the curtain 184 comprises at least one bend 190, positionedbetween the first end 186 and the second end 188 to define first andsecond flexures 192, 194 that allow vertical movement of the supportassembly 138. Although the curtain 184 in FIG. 2 comprises only one bend190, multiple bends 190 may be formed in the curtain 184 to form anaccordion-like structure as shown in FIG. 7. The bends 190 arepositioned below the polygonal substrate support assembly 138 and areoriented substantially parallel to the edge of the support assembly 138to which the second end 188 of the curtain 184 is attached. The bends190 are pre-formed in the curtain 184 to increase the useful life of thecurtain 184; repeated stress transmitted into the curtain 184 byvertical movement of the support assembly 138 might otherwise cause thebends 190 to crack, necessitating replacement of the curtain 184.

[0043] The curtain 184 further comprises at least one lift pin aperture208 a formed in the first flexure 192 and at least one lift pin aperture208 b formed in the second flexure 194. The apertures 208 a, 208 b maybe slots or other shaped openings. Typically, apertures 208 a, 208 b arepositioned equidistant from the bend 190 so that the apertures 208 a,208 b are aligned to allow the lower end 164 of a lift pin 150 to passtherethrough. The apertures 208 a, 208 b are therefore larger indiameter than the lift pins 150. As the substrate support assembly 138is lowered vertically, the bottom ends 164 of the lift pins 150 comeinto contact with the bottom 108 of the chamber 102, which urges thepins 150 through the apertures 208 a, 208 b in the curtains 184 and theholes 128 in the body 124. Furthermore, actuation of the lift pins 150by the bottom 108 of the chamber 102, instead of by a lift plate as usedin conventional systems, allows the bends 190 of the curtain 184 toproject inwardly from the perimeter of the substrate support assembly138, into the space beneath the support assembly 138 (i.e., becausethere is no lift plate beneath the support assembly 138). Therefore,substantially the entire curtain 184 may be positioned beneath thesupport assembly 138, while still maintaining electrical contact withsubstantially the entire perimeter of the support assembly 138. In thisway, the overall system may be manufactured more compactly and withfewer total components.

[0044] During processing, temperatures in the chamber 102 can range from100 to 130 degrees Celsius near the chamber bottom 108, to upwards of350 degrees Celsius on the surface of the support assembly 138 that isin contact with the substrate 140 during processing. Therefore, thesecond end 188 of the curtain 184, which is coupled to the supportassembly 138, would normally be subject to a much greater degree ofthermal expansion than the first end 186 of the curtain 184. Suchvariations in expansion could cause the curtain 184 to deform, impactingthe functionality and the useful life of the curtain 184 in anundesirable way. To counteract the thermal differentials, at least oneperforation 206 is formed in the curtain 184 proximate the second end188 to allow for thermal expansion of the curtain 184. In oneembodiment, a plurality of perforations 206, each having a width ofapproximately 0.8 inch, are spaced approximately every two inches alongthe second end 188 of the curtain 184.

[0045]FIGS. 5 and 6 illustrate the features of the curtain 184 and aconnection assembly 322 in greater detail. The curtain 184 furthercomprises a first mounting flange 202, formed at the first end 186 ofthe curtain 184, and a second mounting flange 204, formed at the secondend 188 of the curtain 184. As with the bends 190, the mounting flanges202, 204 are optionally pre-formed into the curtain 184 and are orientedsubstantially parallel to the edges of the polygonal substrate supportassembly 138 to which the mounting flange 204 is attached. In oneembodiment, the first mounting flange 202 is secured between the bottom108 and a clamp bar 220. The clamp bar 220 and mounting flange 202extend in a direction that is substantially parallel to the edge of thesubstrate support assembly 138 beneath which the clamp bar 220 andmounting flange 202 are positioned. The first mounting flange 202further comprises at least one fastener hole (610 in FIG. 6) that isadapted to receive at least one fastener (not shown) disposed throughthe clamp bar 220, curtain 184 and chamber wall 108 to secure thecurtain 184 in place.

[0046]FIG. 3 depicts the second mounting flange 204 in greater detail.In one embodiment, the second mounting flange 204 is secured to thesupport assembly 138 by a connection assembly 322. The connectionassembly extends substantially parallel to an edge of the supportassembly 138 to which the connection assembly 322 is coupled. Theconnection assembly 322 comprises a vent ring 324 that is coupled to thelower side 126 of the body 124 and an extension block 326 that iscoupled between the clamp ring 324 and a contour block 328. The secondmounting flange 204 is substantially U-shaped to pass over a curvedsurface 330 of the contour block 328, around a curved outer surface 332of the extension block 326, and between substantially flat surfaces 334,336 of the extension block 326 and the vent ring 324. The “U” portion ofthe second mounting flange 204 is substantially parallel to the edge ofthe support assembly 138 to which the mounting flange 204 is coupled.The vent ring 324, the extension block 326 and the contour block 328each further comprises at least one fastener hole (not shown), and thesecond mounting flange 204 comprises at least one set of fastener holes(612 in FIG. 6) aligned and adapted to receive at least one fastener340, such as a mounting screw, disposed through the second mountingflange 204 and the connection assembly 322.

[0047]FIG. 4 depicts one embodiment of the vent ring 324. The vent ring324 comprises a plurality of vent paths 400 formed in the vent ring 324and adapted to allow gas to flow therethrough. The vent paths 400 in thevent ring 324 allow the gases to pass through the connection assembly322 to the area below the substrate support assembly 138. The cornersections 402 of the vent ring 324 optionally include bevel passages 404,i.e., passages cut at an angle relative to the sides of the support body124 to enhance uniform gas passage through the vent ring 324.

[0048]FIG. 8 is a cross sectional view of another embodiment of aprocessing system 800 in which a gas exhaust port 894 is disposed in thebottom 808 of the chamber 802, rather than proximate the lid 810. Thesystem 800 is otherwise similar to the system 100 illustrated in FIG. 1and generally includes a gas source 804 and power source 822 coupled tothe chamber 802. The chamber 802 has sidewalls 806, a bottom 808 and alid assembly 810 that define a process volume 812. The system 800 has aground curtain 884, configured as described herein and disposed betweena substrate support assembly 838 and a grounded chamber 802.

[0049] A vent ring 324 such as that illustrated in FIG. 4 isparticularly ideally suited for use in the system 800. Vent paths 400 inthe vent ring 324 would allow gases to pass from the region above thesubstrate support assembly 838 to the exhaust port 894, despite thepresence of the curtain 884 that extends around substantially the fullperimeter of the support assembly 838.

[0050]FIG. 9 is a cross sectional view of another embodiment of aprocessing system 900 having a ground curtain 984 disposed between asubstrate support assembly 938 and a grounded chamber 902. The system900 is similar to the system 100 illustrated in FIG. 1 and generallyincludes a gas source 904 and power source 922 coupled to the chamber902. The chamber 902 has sidewalls 906, a bottom 908 and a lid assembly910 that define a process volume 912.

[0051] A heated substrate support assembly 938 is centrally disposedwithin the chamber 902. The substrate support assembly 938 may bedisposed at a fixed elevation relative to the chamber bottom 908. Thesupport assembly 938 supports the large area glass substrate 940 duringprocessing. The substrate support assembly 938 generally is similar tothe support assembly 138 illustrated in FIG. 1; however, in theembodiment illustrated in FIG. 9, the support assembly 938 is fixedrelative to at least one of the bottom 908 or the sidewalls 906 of thechamber 902.

[0052] A distribution plate 918 is disposed above the substrate supportassembly 938 and is coupled to a lift 990 that moves the distributionplate 918 vertically relative to the support assembly 938 to control thespacing between the substrate support assembly 938 and the distributionplate 918 during processing. The distribution plate 918 is coupled tothe power source 982 that energizes the distribution plate 918 with RFpower during processing.

[0053] The support assembly 938 has a plurality of apertures 928disposed therethrough that accept a plurality of lift pins 950. The liftpins 950 may be actuated relative to the support assembly 938 by a liftplate 954 to project from the support surface 930, thereby placing thesubstrate 940 in a spaced-apart relation to the support assembly 938.The lift plate 954 is coupled to an actuator 958 by a rod 956 thatextends through the bottom 908 of the chamber 902. The actuator 958enables the lift plate 954 to be moved vertically relative to thesupport assembly 938, thereby engaging the lift pins 950 and urging thelift pins 950 through the apertures 928. The lift plate 954 may beshaped to engage lift pins 950 a, 950 b of varying lengthssimultaneously, or may be flat to engage the lift pins 950 a, 950 b inseveral stages. A bellows 960 surrounds the rod 956 to prevent leakageinto chamber 902 under vacuum conditions. The lift plate 954 furthercomprises a plurality of vent holes 970 to allow gases to passtherethrough.

[0054] Because the support assembly 938 is fixed, the RF ground curtain984 is not required to flex or accommodate motion, as is the groundcurtain 184 illustrated in the previous Figures. Therefore, a curtain984 may be advantageously adapted to extend continuously around the fullperimeter of the stationary support assembly 938 wherein the curtain 984is not required to flex to accommodate substrate support movement. Thecurtain 984 may be cylindrical or linear in form and is not required tohave a bend or bends. The curtain 984 is otherwise substantially similarto the curtain 184, having a first end 986 electrically connected to thechamber bottom 908 and a second end 988 that is connected to the supportassembly 938. The curtain 984 comprises first and second mountingflanges 903, 905, configured as described herein, and secured to thewall 908 and support assembly 938 by a clamp bar and connection assemblysuch as those previously illustrated. Perforations for thermal expansionare cut into the second end 988 of the curtain 984.

[0055] Thus, the present invention represents a significant advancementin the field of large area substrate processing. An apparatus isprovided that significantly limits voltage drops in an RF current returnpath and is suitable for use in large scale processing systems such asthose used to fabricate flat panel and liquid crystal displays.Furthermore, the apparatus is manufactured for improved functionalityand durability, incorporating integral features that limit cracking anddeformations caused by repeated stress and exposure to heat.

[0056] While the foregoing is directed to embodiments of the invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. An apparatus for providing an RF current returnpath between a chamber body and a substrate support, comprising: a lowimpedance flexible curtain having a first end and a second end, thefirst end adapted to be electrically connected to the chamber body andthe second end adapted to be electrically connected to the substratesupport, wherein the curtain further comprises: at least one bendlocated between the first end and the second end; a first flexureextending from the at least one bend toward the first end; a secondflexure extending from the at least one bend toward the second end; andat least one perforation formed through the flexure coupled to thesecond end.
 2. The apparatus of claim 1, wherein the curtain furthercomprises: at least one aperture formed in the first flexure; and atleast one aperture formed in the second flexure, wherein the aperturesin the first and second flexures are aligned equidistantly from the atleast one bend.
 3. The apparatus of claim 1, wherein the flexures aresubstantially quadrilateral in shape.
 4. The apparatus of claim 1,wherein the first end of the curtain is at least twelve inches wide. 5.The apparatus of claim 1, wherein the curtain comprises at least one ofaluminum or an aluminum coating.
 6. The apparatus of claim 1, whereinthe first end of the curtain comprises a first mounting flange thatextends substantially parallel to the at least one bend in the curtain.7. The apparatus of claim 6, wherein the first mounting flange isadapted to be secured between the chamber body and a clamp bar.
 8. Theapparatus of claim 7, wherein the first mounting flange furthercomprises at least one fastener hole adapted to receive at least onefastener disposed through the clamp bar, curtain and chamber body. 9.The apparatus of claim 1, wherein the second end of the curtaincomprises a second mounting flange that extends substantially parallelto the at least one bend in the curtain.
 10. The apparatus of claim 9,wherein the second mounting flange is adapted to be secured to thesubstrate support by a connection assembly.
 11. The apparatus of claim10, wherein the connection assembly comprises: a vent ring adapted to becoupled to the substrate support; an extension block, a first surface ofwhich is adapted to be coupled to the vent ring; and a contour blockadapted to be coupled to a second surface of the extension block. 12.The apparatus of claim 11, wherein the second mounting flange issubstantially U-shaped and adapted to pass between the contour block andextension block, around an outer surface of the extension block, andbetween the extension block and the vent ring.
 13. The apparatus ofclaim 11, wherein the second mounting flange further comprises at leastone set of aligned fastener holes adapted to receive at least onefastener disposed through at least two of the contour block, curtain,extension block, vent ring and substrate support.
 14. The apparatus ofclaim 11, wherein the vent ring comprises a plurality of vent paths. 15.The apparatus of claim 14, wherein at least one of the plurality of ventpaths is a bevel passage positioned in a corner section of the ventring.
 16. A substrate processing chamber comprising: a chamber body; asubstrate support disposed in the chamber body and having asubstantially polygonal support surface; and a low impedance flexiblecurtain having a first end and a second end, the first end beingelectrically connected to a chamber wall and the second end beingelectrically connected to the substrate support, wherein the curtainfurther comprises: at least one bend located between the first end andthe second end; a first flexure extending from the at least one bendtoward the first end; a second flexure extending from the at least onebend toward the second end; and at least one perforation formed throughthe flexure coupled to the second end.
 17. The chamber of claim 16,wherein the flexures are substantially quadrilateral in shape.
 18. Thechamber of claim 16, wherein the flexures are adapted to allow verticalmotion of the substrate support relative to the chamber wall.
 19. Thechamber of claim 16, wherein the curtain is adapted to be coupled to atleast one edge of the substrate support.
 20. The chamber of claim 19,wherein the curtain extends continuously around a full perimeter of thesubstrate support.
 21. The chamber of claim 16, wherein the curtainfurther comprises at least one aperture formed in the first flexure; andat least one aperture formed in the second flexure, wherein theapertures in the first and second flexures are aligned equidistantlyfrom the at least one bend.
 22. The chamber of claim 21, wherein thesubstrate support further comprises at least one lift pin disposedvertically through the substrate support and apertures.
 23. The chamberof claim 22, wherein the at least one lift pin is urged verticallythrough the apertures and the substrate support by contact with a bottomof the chamber.
 24. The chamber of claim 16, wherein the curtaincomprises a plurality of bends.
 25. The chamber of claim 16, wherein thechamber is a chemical vapor deposition chamber.
 26. A substrateprocessing chamber comprising: a chamber body; a substrate supportdisposed in the chamber body; a vertically movable gas distributionplate coupled to a lid of the chamber; and a low impedance flexiblecurtain having a first end and a second end, the first end beingelectrically connected to a chamber wall and the second end connected tothe substrate support, wherein the curtain further comprises: a firstmounting flange adapted to secure the first end to the chamber body; asecond mounting flange adapted to secure the second end to the substratesupport; at least one perforation formed through the curtain proximatethe second end.
 27. The chamber of claim 26, wherein the curtain isadapted to be coupled to at least one edge of the substrate support. 28.The chamber of claim 27, wherein the curtain extends continuously arounda full perimeter of the substrate support.
 29. The chamber of claim 26,wherein the curtain is substantially quadrilateral in shape.
 30. Thechamber of claim 26, wherein the chamber is a chemical vapor depositionchamber.
 31. A substrate processing chamber comprising: a chamber body;a substrate support disposed in the chamber body; and a low impedanceflexible curtain having a first end and a second end, the first endbeing electrically connected to a chamber wall and the second endconnected to the substrate support, wherein the curtain furthercomprises: at least one bend in the curtain material, located betweenthe first end and the second end, the bend projecting inwardly from aperimeter of the substrate support toward a center of the substratesupport.
 32. The chamber of claim 30, wherein the curtain furthercomprises: a first flexure extending from the at least one bend towardthe first end; a second flexure extending from the at least one bendtoward the second end; and at least one perforation formed through aflexure coupled to the second end.
 33. The chamber of claim 32, whereinthe flexures are substantially quadrilateral in shape.
 34. The chamberof claim 31, wherein the curtain comprises: at least one aperture formedin the first flexure; and at least one aperture formed in the secondflexure, wherein the apertures in the first and second flexures arealigned equidistantly from the at least one bend.
 35. The chamber ofclaim 31, wherein the substrate support further comprises: a pluralityof apertures disposed through the substrate support; a plurality ofsubstrate lift pins disposed through the plurality of apertures, whereinthe plurality of lift pins is urged vertically through the apertures bycontact with the chamber body.
 35. The chamber of claim 31, wherein thecurtain is adapted to be coupled to at least one edge of the substratesupport.
 36. The chamber of claim 31, wherein the curtain extendscontinuously around substantially a full perimeter of the substratesupport.
 37. The chamber of claim 31, wherein the curtain comprises aplurality of bends.
 38. The chamber of claim 31, wherein the chamber isa chemical vapor deposition chamber.